1. Field of the Invention
The present invention relates to a high-molecular thin film having a fine structure obtained by microphase separation of block copolymers on a substrate surface, a pattern medium obtained by utilizing the high-molecular thin film, and a manufacturing method of those.
2. Description of the Related Art
In recent days, a formation of a fine ordered array pattern with a size of several nm to several hundred nm on a substrate becomes highly requisite together with downsizing of electronic devices, energy storage devices, sensors and the like and with advancement of the performances thereof. Accordingly, processes of manufacturing such a fine pattern structure with high precision and low cost must be established.
A general example of a method of fabricating such a fine pattern is a top-down method represented by lithography, i.e., a method of chipping a bulk material minutely to form a shape. For example, photolithography applied in semiconductor microfabrication for manufacturing of an LSI or the like is a representative example.
However, as the level of fineness increases, an application of such a top-down method gives difficulties relating to both apparatus and process. In particular, as the fabrication size of a fine pattern becomes so fine in several ten rim, electron beams and deep ultraviolet become requisite, resulting in huge investment for apparatuses. Also, as formation of a fine pattern using a mask becomes difficult, direct plotting must be applied, so that it becomes difficult to avoid a problem that the fabrication throughput significantly decreases.
Getting attention under such circumstances is a process utilizing a phenomenon that substances naturally form a structure, i.e., a so-called self-assembly phenomenon. In particular, a process utilizing the self-assembly phenomenon of block copolymers, i.e., a so-called microphase separation is superior from the standpoint of its capability of formation of a fine regular structure having various kinds of shapes in several ten nm to several hundred nm by a simple application process. For example, when various kinds of high-molecular segments constituting block copolymers do not mix one another (immiscible), a fine structure having a specific regularity is self-assembled by phase separation (microphase separation) of those high-molecular segments.
An example of formation of such a fine regular structure by utilizing a self-assembly phenomenon is a conventionally well-known technology of using a block copolymer thin film, composed of combinations of polystyrene and polybutadiene, polystyrene and polyisoprene, polystyrene and polymethylmethacrylate, and the like, as an etching mask, and of forming structures, such as a pore, and a line-and-space, on a substrate.
According to such microphase separation phenomenon of block copolymers, it is possible to obtain a high-molecular thin film having a structure in which fine spherical, cylindrical, and lamella microdomains that are difficult to obtain by the top-down method are arranged regularly.
In general, application of a self-assembly phenomenon including microphase separation to patterning has, however, following problem.
Patterning utilizing a self-assembly phenomenon has a superior short-range regularity but has a poor long-range orderliness, so that defects and grain boundaries are present and formation of an arbitrary pattern is difficult. In particular, because self-assembling utilizes a structure formed by nature, i.e., a structure that has smallest energy, it is generally difficult to obtain structures other than a regular structure with a period inherent to a material, and because of such restriction, the range of application of patterning is thus limited. In order to overcome such defects, the following two methods are conventionally known.
A first method causes microphase separation to be developed by forming a trench on a substrate surface and by forming block copolymers in the trench. According to such a method, a fine structure developed by the microphase separation is arranged along a wall surface of the trench, so that it becomes possible to control the directionality of the regular structure in one direction, thereby enhancing the long-range orderliness. Also, any generation of defects is suppressed because the regular structure is filled along the wall surface. Such an effect is known as a graphoepitaxy effect. The wider the width of the trench, the less such an effect. When the width of the trench becomes ten times or so as much as the period of the regular structure, disorder is produced in the regular structure at the center of the trench. Also, formation of the trench on the substrate surface is requisite, so that such a method cannot be applied to a case in which a flat surface is necessary. Further, according to such a method, it is possible to orient the regular structure in a direction along the trench, but further arbitrary pattern controlling is not possible.
A second method causes a substrate surface to be chemically patterned, and controls a structure developed by microphase separation due to chemical interaction between the substrate surface and block copolymers (see, for example, U.S. Pat. Nos. 6,746,825 and 6,926,953). FIG. 14 is a conceptual perspective view for explaining a conventional method of causing a substrate surface to be chemically patterned.
As shown in FIG. 14, this method uses a chemically-patterned substrate 305 having a surface thereof patterned by a top-down method in such a way that affinities to each block chain (first polymer block chain 301 and second polymer block chain 302) constituting a block copolymer 303 differ from each other. According to this method, a film of the block copolymer 303 is formed on a surface of the chemically-patterned substrate 305 to develop microphase separation. For example, when a diblock copolymer composed of polystyrene and polymethylmethacrylate is used as the block copolymer 303, a chemical pattern is formed while the surface of the chemically-patterned substrate 305 is divided into an area 307 having a good affinity to polystyrene and an area 308 having a good affinity to polymethylmethacrylate. As the shape of the chemical pattern is conformed to a microphase-separated structure of a polystyrene/polymethylmethacrylate diblock copolymer, a continuous phase 306 formed of polystyrene is arranged on the area 307 having good affinity to polystyrene and a cylindrical microdomain 304 formed of polymethylmethacrylate is arranged on the area 308 having good affinity to polymethylmethacrylate at the time of microphase separation.
That is, according to this method, it is possible to arrange a microphase-separated structure along marks chemically arranged on the substrate surface. Also, according to this method, because the chemical pattern is formed by the top-down method, the long-range orderliness of the pattern obtained is secured by the top-down method, and it is possible to obtain a pattern having good regularity and few defects across a wide range. In the following explanation, this method is called a chemical registration technique of a microdomain in some cases.
According to the conventional chemical registration technique, however, when a process size becomes fine and highly density until several ten nm, any defects and disorder of a pattern shape tend to be produced. This negatively affects a microphase-separated structure to be obtained. Accordingly, it is thought that obtained chemical patterns are arranged discretely relative to locations where microdomains are to be formed, i.e., a microphase-separated structure is formed in such a way that a microdomain is also formed between chemically arranged marks by an interpolation effect of self-assembling.
However, when a ratio between a density of the microdomains and a density of patterns has a relation like n:1 (where n is a number greater than 1), there is a following problem.
That is, when microphase separation of a block copolymer film formed on a substrate surface is developed, a part where a chemical pattern is formed becomes a structure having microdomains upright relative to the substrate, but a part where no chemical pattern is formed has microdomains oriented not upstanding relative to the substrate, so that a high-density pattern having chemical patterns interpolated may not be obtained in some cases. Accordingly, it is difficult to obtain a pattern which does not lose uniform long-range orderliness across the whole area of the chemical pattern and has few defects. In addition, the larger the value of n, the more remarkable this problem.
Therefore, an object of the present invention is to provide a high-molecular thin film having a fine structure composed of a microphase-separated structure with a good long-range orderliness and few defects, a pattern medium obtained by utilizing such a high-molecular thin film, and a method of manufacturing those.